Display controller for bistable electro-optic display

A method of driving a bistable electro-optic display having a plurality of pixels, each pixel being capable of displaying two extreme optical states, the method comprising:

• providing a timer that establishes a minimum time interval between successive applications of refresh pulses to differing non-zero proportions of background pixels;
• writing a first image on the display;
• writing a second image on the display using a drive scheme in which a plurality of background pixels which are in the same extreme optical state in both the first and second images are not driven;
• leaving the display undriven for a period of time, thereby permitting the background pixels to assume an optical state different from their extreme optical state;
• after said period of time, applying to a first non-zero proportion of the background pixels a refresh pulse which substantially restores the pixels to which it is applied to their extreme optical state, said refresh pulse not being applied to the background pixels other than said first non-zero proportion thereof;
• and
• at least 10 seconds after applying the refresh pulse to the first non-zero proportion of the background pixels, applying to a second non-zero minor proportion of the background pixels different from the first non-zero proportion a refresh pulse which substantially restores the pixels to which it is applied to their extreme optical state, said refresh pulse not being applied to the background pixels other than said second non-zero proportion thereof,
• wherein the first and the second non-zero proportions of the background pixels each include at least two pixels.